Recent Progress of Remediating Heavy Metal Contaminated Soil Using Layered Double Hydroxides as Super-Stable Mineralizer.

Heavy metal contamination in soil, which is harmful to both ecosystem and mankind, has attracted worldwide attention from the academic and industrial communities. However, the most-widely used remediation technologies such as electrochemistry, elution, and phytoremediation. suffer from either secondary pollution, long cycle time or high cost. In contrast, in situ mineralization technology shows great potential due to its universality, durability and economical efficiency. As such, the development of mineralizers with both high efficiency and low-cost is the core of in situmineralization. In 2021, the concept of 'Super-Stable Mineralization' was proposed for the first time by Kong et al.[1] The layered double hydroxides (denoted as LDHs), with the unique host-guest intercalated structure and multiple interactions between the host laminate and the guest anions, are considered as an ideal class of materials for super-stable mineralization. In this review, we systematically summarize the application of LDHs in the treatment of heavy metal contaminated soil from the view of: 1) the structure-activity relationship of LDHs in in situ mineralization, 2) the advantages of LDHs in mineralizing heavy metals, 3) the scale-up preparation of LDHs-based mineralizers and 4) the practical application of LDHs in treating contaminated soil. At last, we highlight the challenges and opportunities for the rational design of LDH-based mineralizer in the future.

Insight into the In-Situ Encapsulation-Reassembly Strategy To Fabricate PW12@NiCo-LDH Acid-Base Bifunctional Catalysts.

Acid-base bifunctional catalysts have attracted increasing attention due to the improved overall efficiency of synthetic reactions. Herein, we reported the successful fabrication of a PW12@NiCo-LDH acid-base bifunctional catalyst by using the in-situ encapsulation-reassembly strategy. The evolution process of morphology and structure was monitored carefully by various time-dependent characterizations. X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculations demonstrated that the terminal oxygen of PW12 in PW12@NiCo-LDH preferred to assemble with the oxygen vacancies on NiCo-LDH. When applied for deacetalization-Knoevenagel condensation, the PW12@NiCo-LDH displayed >99% conversion of benzaldehyde dimethyl acetal (BDMA) and >99% yield of ethyl α-cyanocinnamate (ECC). Moreover, PW12@NiCo-LDH can be recycled at least 10 cycles without obvious structural change, which can be attributed to the confinement of PW12 into the NiCo-LDH nanocage. Such excellent catalytic activity of PW12@NiCo-LDH was benefited from the short mass transfer pathway between acid sites and base sites, which was caused by the stable assembly between PW12 and NiCo-LDH.